Controller for coded surface acoustical wave (SAW) security system

ABSTRACT

A controller for a motor vehicle security system. The controller has a SAW device adapted to receive a signal and to generate a reply signal. A decoder is connected to the SAW device for decoding the reply signal. A comparator compares the reply signal to a previously stored value and an enabling device enables operation of the motor vehicle when the predetermined value and the decoded reply signal are successfully compared.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related in subject matter to Ser. No.07/227,282 for "Coded Surface Acoustical Wave (SAW) Motor VehicleSecurity Device", filed concurrently herewith.

BACKGROUND OF THE INVENTION

The present invention relates to a controller for a security system and,more particularly, to a controller for a coded surface acoustical wave(SAW) device that interacts with the ignition system of a motor vehicle.

Motor vehicles are susceptible to theft due to their relative high valueand inherent transportability. Automobiles and trucks are especiallyattractive as objects of theft, as evidenced by an alarmingly high theftrate in many civilized countries.

The simplest security device has been the ignition key, which isrelatively unique for each automobile corresponding thereto. However,professional thieves now duplicate such mechanical keys, by-passignition switches and/or remove the ignition apparatus from automobilesaltogether in order to jump start them.

Heretofore, most systems for preventing theft of automobiles have beenrelegated to audible alarms signaling the attempted theft or break-in ofthe protected automobile. Certain mechanical and/or electronicinterlocking devices have made it difficult for an automobile to bestolen by means of a standard ignition key alone. One such mechanicaldevice comprises a tumbler lock and bar adapted to retain a steeringwheel in a fixed position. The use of that system is, of course,cumbersome as well as time consuming.

Another interlocking device is a mechanical ignition key that containsresistive elements. Unfortunately, that system requires direct physicaland electrical contact between the key and the electric sensor, whichcontact cannot always be guaranteed.

Recently, surface acoustic or acoustical wave (SAW) devices have beenused to label certain items, such as objects for sale in retailestablishments and individual inventory parts in warehouses. A SAW labelsystem generally includes an interrogator for transmitting a first radiofrequency (RF) signal and a SAW transponder which receives the signal,processes it and sends back a second RF signal containing encodedinformation. A receiver receives the second signal and decodes theinformation.

The transponder is nonpowered or passive. It receives the first(interrogating) signal as an input and produces the second (reply)signal as an output. Passive signal transforming means, within thetransponder, converts the first signal to the second signal.

The transforming means includes signal conditioning elements coupled toreceive the first signal from a transponder antenna. Each signalconditioning element provides an intermediate signal having a knowndelay and a known amplitude modification to the first signal. Thetransforming means also includes a signal combining element coupled toall of the signal conditioning elements for combining intermediatesignals by addition or by multiplication to produce the second signal.The signal conditioning elements and the signal combining element imparta known informational code to the second signal which identifies theparticular transponder. The second signal can be coupled out of the sameantenna or a separate antenna for transmission as a reply.

Radiation, picked up by the antenna, is converted into electricalsignals which are, in turn, converted into surface acoustic waves on theSAW device by a so-called leading transducer. These waves traveloutwardly in opposite directions from opposite sides of the leadingtransducer and are then reconverted into electrical signals.

The aforementioned system is described in greater detail in U.S. Pat.No. 4,737,790 issued to Skeie et al. The system disclosed therein uses avoltage controlled oscillator to produce the first signal.

U.S. Pat. No. 4,625,208 issued to Skeie et al discloses a passivetransponder for use in an interrogation system. A circuit is connectedto transducer elements for supplying interrogating signals to thetransducer elements and for receiving reply signals therefrom. Acousticwave reflectors are provided to reflect the surface acoustic waves backtowards the transducer elements.

As mentioned above, the systems disclosed in the aforementioned patentsinclude a transmitter capable of transmitting RF pulses ofelectromagnetic energy. These pulses are received at the of thetransponder and applied to a piezoelectric leading transducer adapted toconvert the electrical energy received from the antenna into acousticwave energy in the piezoelectric material. Upon receipt of a pulse, anacoustic wave is generated within the piezoelectric material and istransmitted along a defined acoustic path.

Further transducers arranged at prescribed spaced intervals along thisacoustic path convert the acoustic wave back into electrical energythereby re-exciting the antenna of the transponder The presence orabsence of transducers at the prescribed locations along the acousticwave path determines whether a reply pulse will be transmitted with aparticular time delay in response to an interrogation pulse. Thisdetermines the informational code contained in the transponder reply.

When an acoustic wave pulse is reconverted into an electrical signal, itis supplied to an antenna on a transponder and transmitted as RFelectromagnetic energy. This energy is received at a receiver anddecoder, preferably at the same location as the interrogatingtransmitter, and the information contained in the response is decoded.

If SAW technology could be used for purposes other than mereidentification of items, a significant improvement in security ofvaluable objects such as motor vehicles could be achieved.

A sophisticated security device is required for helping to ensure thatan automobile may not be started and driven by on not authorized to doso.

It would be advantageous to provide a motor vehicle security system thatwould make it impossible to start the vehicle by using an unauthorizedignition key, or by by-passing the ignition switch or even by removingthe switch assembly.

It would also be advantageous to provide a security system which doesnot require an electrical source of supply such as an electric battery.

It would also be advantageous to provide a security system which doesnot require electrical contact.

It would be advantageous to provide a SAW-based security system fordiscouraging theft of motor vehicles.

It would further be advantageous to provide a SAW-based securityinterlock system in the form of an ignition key.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a controllerfor a motor vehicle system. The controller has a SAW device adapted toreceive a signal and to generate a reply signal. A decoder is connectedto the SAW device for decoding the reply signal. A comparator comparesthe reply signal to a previously stored value and an enabling deviceenables operation of the motor vehicle when the predetermined value andthe decoded reply signal are successfully compared.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the present invention may be obtained byreference to the accompanying drawings, when taken in conjunction withthe detailed description thereof and in which:

FIG. 1 is a perspective view of a steering column, steering wheel andcomputer processor;

FIG. 2 is an exploded perspective assembly view of the preferredembodiment of the present invention;

FIG. 3 is a cross sectional view of a key inserted in an ignitionswitch;

FIG. 4 is a schematic representation of a key with a SAW device insertedin proximity to a coupling coil;

FIG. 5 is a schematic representation of a key with a SAW device imbeddedtherein;

FIG. 6 is a representation of a SAW device shown connected to a couplingcoil;

FIG. 7 is an exploded plan view of a SAW device;

FIG. 8 is a schematic circuit diagram of digital logic used in thepresent invention;

FIG. 9 is a schematic diagram of an analog circuit used to generate apulse and to provide receiving and amplifying functions;

FIG. 10 is a flow chart showing operation of the invention by anoperator of a motor vehicle; and

FIGS. 11 and 12 are timing diagrams representing FIG. 8 circuitoperation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there are shown a conventional steering wheel10 and steering column 12, as can be found in most motor vehicles andespecially in automobiles. Connected to an ignition switch 14,hereinbelow described in greater detail, is a microprocessor 16. Manymotor vehicles have electronic brains or computer processors such asthat shown as reference numeral 16, used to regulate the electrical,mechanical and chemical systems used in the vehicles. Often, generalpurpose computers, a network thereof, or microprocessor-based electronicsystems are used for the various functions. For example, a computerprocessor in an automobile may be used to regulate gas flow, to signalmalfunctions in brake systems, to indicate the level of oil in thecrankcase, to adjust internal temperature and the like.

A collar housing 18 is shown mounted on the steering column 12 by meansof screws 20, although any suitable mounting means may be used for thispurpose. The collar 18 houses a coupling coil or antenna, not shown, theuse of which is explained hereafter. Certain circuitry may also becontained within the collar 18.

Referring now also to FIG. 2, there is shown a perspective assembly viewof the preferred embodiment of the present invention. The collar housing18 has a circular aperture 19 cut therein. A printed circuit board orcard 22 is housed by the collar housing 18 and encircles the ignitionswitch, not shown. The printed circuit board 22 has components mountedthereon that function as a receiver in cooperation with a SAW device ashereinbelow described. Encircling the printed circuit board aperture isa coupling coil 24, the use of which is described in greater detailhereinbelow.

An ignition key is shown generally at reference numeral 26. The key 26is adapted to be inserted through the collar aperture 19 and into theignition switch, not shown. It should be noted that a conventionalignition key with a coded mechanical blade is not necessarily arequirement of the present invention.

Referring now also to FIG. 3, there is shown a cross sectional side viewof an ignition key 26 inserted into the ignition switch 14.

Referring now also to FIG. 4, there is shown a schematic representationof an ignition key 26, the outline of which is shown in phantom. In thepreferred embodiment, the key 26 has a longitudinal mechanicalprotuberance 28, as do most conventional ignition keys. Thislongitudinal section 28 is preferably fabricated of metal and ismechanically coded to fit a particular ignition key lock, not shown.

Connected to the metal protuberance 28 is a key handle 30. The handle 30has an aperture 32 adapted to fit onto conventional key holders and keyrings, not shown. The handle 30 can be rubber, plastic or any othersuitable nonmetallic material. Plastic is preferred. Imbedded in thehandle 30 is a surface acoustical wave (SAW) device 34. Connected to theSAW device 34 is a coupling coil or antenna 36. The coil 36 forms acontinuous loop connected to the SAW device 34 at ports 38 and 40 and isdisposed perpendicular to the major axis of the key 26 and the SAWdevice 34.

Also shown in FIG. 4 is a second coupling coil or antenna 42, whichencircles the SAW device coil 36, but is not connected thereto. Thesecond coil 42 is connected to a sensor, not shown, by means of anelectrically conductive cable 44. It can be seen that the key 26 and SAWdevice coil 36 are adapted to move relative to the second coil 42.

Referring now also to FIG. 5, there is shown another cross sectionalview of an ignition key in accordance with the present invention. Inthis embodiment, the SAW device coil 36 is disposed parallel to themajor plane of the key 26 and of the SAW device 34. This coilconfiguration can also be used with appropriate modification to thesensor coil 42 (FIG. 4).

Referring now also to FIG. 6, there is shown a representation of a SAWtransponder, which is imbedded in an ignition key 26 and to which isconnected a coupling coil 36. It should be noted that other coil orantenna configurations, such as dipole antennas, can also be used.

The transponder operates to convert a received signal to an acousticwave and then to reconvert the acoustic energy back into an electricalsignal for transmission via the coupling coil 36. The signaltransforming element of the transponder includes a substrate ofpiezoelectric material, not shown, on one surface of which is depositeda layer of metal, such as aluminum, forming a 6-bit spatial pattern ofelectrodes or transducers shown in FIG. 6. In alternate embodiments,binary codes of more or less than six bits can be used. Moreover, thecode itself need not necessarily be binary.

The piezoelectric substrate, not shown, is fabricated from YZ lithiumniobate (LiNbO₃). Other materials can be used for the piezoelectricsubstrate, such as PZT ceramic and PVDF polymers.

The aforementioned transducer pattern comprises two bus bars 62 and 64connected to the coupling coil 36. A leading transducer 50 and aplurality of coding elements or tap transducers 52, 54, 56, 58, 60, 61are also provided. These transducers are also known as interdigitatedelectrode arrays. The bus bars 62 and 64 define a path of travel, shownby arrow 66, for an acoustic wave which is generated by the leadingtransducer 50 and propagates substantially linearly, reaching the taptransducers 52-61, each in turn. The tap transducers 52-61 convert theacoustic wave back into electrical energy which is collected andtherefore summed by the bus bars 62 and 64. This electrical energy thenactivates the coupling coil 36 and is converted into electromagneticradiation for transmission.

In the preferred embodiment, the tap transducers 52-61 are provided atequally spaced intervals along the acoustic wave path 66. Aninformational code associated with the transponder can be imparted byremoving a selected number of tap transducers 52-61. In alternateembodiments, delay pads, not shown, can be provided between taptransducers 52-61. They can be made of the same material as, anddeposited with, the bus bars 62 and 64 and the tap transducers 52-61,each delay pad having a width sufficient to delay the propagation of theacoustic wave from one tap transducer 52, for example, to the next 54.

The use of irregularly shaped delay pads, not shown, would make itpossible to control the amplitude as well as the phase of the acousticwave. Such amplitude modification may be detected by a receiver orsensor and decoder system so that additional codes may be imparted inthe transponder without requiring additional tap transducers and delaypads.

Referring now also to FIG. 7, an exploded view of the transponder ofFIG. 6 is shown with leading transducer 50 and the set of taptransducers 52, 54, 56, 58, 60, 61 consisting of a total of 200electrodes. At least two versions are available on the photomask: asingle electrode and a double (or split) electrode. The split electrodeversion of the preferred embodiment has 400 electrodes spaced at quarterwavelengths, resulting in 40 interdigitated electrodes per transducer.The latter configuration provides freedom to vary bit rate and bit size.SAW devices can be fabricated and customized by using conventionalphotolithography means well known in the art.

Alternate electrodes are connected to different conductors by means ofthe bus bars 62 and 64. The spacing of the electrodes is approximately38.68 μm. The precise distance is adjusted to be one half of awavelength of a surface electroacoustic wave at the operating centerfrequency of 44.33 MHz. The bit size is 10 cycles per bit, resulting ina bit rate of 4.433 MHz. Modulation is by amplitude (AM), pulsepresence. The desired code is carried by the array by means ofconnecting or disconnecting an array element 52-61 at a given point onthe bus bars 62 and 64, signifying respectively a one or a zero binarydigit.

In practice, all keys are manufactured with a full sequence of ones byhaving all array elements present. The required code is impressed on thekey by severing the connection of an appropriate number of arrayelements from the bus bars 62 and 64. One process for severing theinterdigitated electrodes by means of standard photolithographicprocessing known in the art.

It should also be understood that, although pulse presence in coding ispreferred, the system described can likewise be operated with pulsewidth modulation or pulse position modulation. The latter twoalternatives, however, require more bits for the same number of codes.Handling more bits on the same chip requires more transducer fingers andfewer cycles per bit. This tends to reduce signal level and can increasespurious levels.

In the preferred embodiment, the modulation scheme uses six bits, withthree and only three bits always being present. A parity check cantherefore be performed to ensure that three bits are set. With 20half-cycles per bit and an active SAW area restricted to a length of 8mm, there is room on the chip for nine bits. The restriction to 8 mm iscompletely arbitrary, but some limitation has to be made forpracticality and economy. The aforementioned 6-bit code is implementedin the last six of the nine bits; the first three bits are always set to0 to reduce crosstalk.

Twenty codes are possible in the 3/6 modulation scheme. They areassigned values arbitrarily as shown in Table I.

                  TABLE I                                                         ______________________________________                                        Six-Bit Codes                                                                         Index Code                                                            ______________________________________                                                1     111000                                                                  2     110100                                                                  3     110010                                                                  4     110001                                                                  5     101100                                                                  6     101010                                                                  7     101001                                                                  8     100110                                                                  9     100101                                                                  10    100011                                                                  11    011100                                                                  12    011010                                                                  13    011001                                                                  14    010110                                                                  15    010101                                                                  16    010011                                                                  17    001110                                                                  18    001101                                                                  19    001011                                                                  20    000111                                                          ______________________________________                                    

Referring now also to FIG. 8, logic circuitry is shown. A CMOSintegrated circuit (IC) 120, available from RCA Corporation as Model No.4060, comprises an oscillator and a multistage divider. Connected to theIC 120 is a crystal 168 for providing a fixed frequency. In thepreferred embodiment, the base frequency of the system is 44.33 MHz. TheIC 120 has a number of output ports, three of which (Q5, Q9 and Q10) aredescribed in greater detail hereinbelow.

Two integrated circuit chips 122 and 124 are used as a counter and areconnected to IC 120. Also connected to IC 120 are two flip flops 150 and162. NAND gates 148 and 160 are disposed intermediate the IC 120 and theflip flops 150 and 162, respectively.

Another NAND gate 154 receives inputs from a flip flop 152 and datagenerated by circuitry on the circuit board (FIG. 2) which functions asa receiver. Connected to flip flop 152 is a shift register 134 capableof strobing at least six ports (Q0-Q5) in parallel to respectiveinverters 190, 192 et al.

Also connected to the register 134 is another integrated circuit device136 which is capable of counting bits. The output from the bit counter136 is applied to NAND gate 178 and to inverter 180. Subsequently, thesignal inverted by inverter 180 is NANDed with the six bit signals frominverters 190, 192 et al by NAND gate 138. NAND gate 138 is connected toa pair of flip flops 140 and 142 which, in turn, are connected to NANDgate 144, inverter 146, NAND gate 148 and flip flop 150.

The counter 122 and 124 is connected to inverters 126 and 128. Theoutputs from these inverters 126 and 128 are applied to a NAND gate 130which, in turn, is applied to inverter 132. The output of inverter 132is applied to register 134.

An inverter 182 is connected to the counter 122 and 124 and the outputthereof is applied to a pulser, as described in further detail withregard to FIG. 9, below.

In operation, the crystal 168 connected to the oscillator 120 forms asystem clock, the frequency of which is the same as the data rate of theSAW device. The dividers of the IC 120 provide other system timing.Diode 172, resistor 174 and capacitor 176 perform an initializationfunction through gate 156, to ensure that the outputs Q5, Q9 and Q10 ofIC 120 all start at logic low.

The divide by 512 output Q9 of divider 120 starts low and is applied tothe reset R ports of ICs 140, 142, and 150, holding them in a resetmode. This function disables the system for the first half of the divideby 512 cycle, allowing time for the bias in the analog circuits (FIG. 9,below) to reach equilibrium. During the second half of the divide by 512cycle, the system operates as described below.

The divide by 32 output Q5 of divider 120 cycles eight times during adivide by 512 half cycle. Each high state constitutes a read cycle. TheQ5 signal is inverted by device 182 and fed to a pulse circuit, notshown, which excites the key 26 (FIG. 4) at the start of the read cycle.The output of port Q5 of divider 120 is applied to LOAD ports of counterICs 122 and 124. The low state of the Q5 signal thus preloads thecounter 122 and 124.

When the Q5 signal is high, the counter 122 and 124 runs to terminalcount and latches via devices 126 and 128. These two signals generatedby devices 126 and 128 are gated together in device 130 and inverted byinverter 132 to generate a "read window" which is high only when abinary code is being transferred from the SAW device. This read windowis used to enable the shift register 134, so that the register 134 loadsdata serially only at the proper time.

The data that loads into register 134 is generated by a synchronousdetector comprising flip flop 152 and NAND gate 154. The NAND gate 154has applied thereto data from the receiver (FIG. 2). Since the systemclock has the same rate as does the SAW device, they can be gatedtogether in device 154 and shaped by flip flop 152. This minimizesambiguity in converting an analog coded signal to digital logic levels.

The data that loads into register 134 is also applied to counter 136.This counter 136 and gate 178 form a bit counter, which counts thenumber of logic high bits, providing an error check function.

The parallel output of register 134 from ports Q0-Q5 is inverted or notinverted, depending upon the code in the data. This mechanismfacilitates programming the system for different codes. The paralleloutput Q0-Q5 is gated, along with the output of bit counter 136, in the8-input NAND gate 138. If the code matches the program and contains thecorrect number of high bits, the output of gate 138 goes low, signifyinga correct read and successful match.

Flip flops 140 and 142 form a 2-bit counter, shown generally atreference numeral 143. The output of the counter 143 is gated in device144 so that the gate output goes low for a count of 3. This counter 143is driven by the correct read signal so the output of gate 144 indicatesthat three correct reads have been performed.

The output of gate 144 is inverted in inverter 146 and gated with the Q9signal of divider 120 in NAND gate 148. When the system is enabled andthree correct reads have occurred, the output of device 148 goes low,which sets flip flop 150, causing its Q output to go high, generating aVEHICLE START ENABLE signal, allowing the operation of the vehicle, notshown. This high VEHICLE START ENABLE signal is also inverted byinverter 158. Diode 170 clamps the clock oscillator in IC 120, causingthe system to be dormant until initialized again.

If three correct reads do not occur, then the Q output of IC 150 will behigh. At the end of the enable cycle, the Q10 signal of IC 120 goeshigh. These two signals are gated in NAND gate 160 and flip flop 162 isset. The Q output of flip flop 162 then goes high, enabling IC 166 and,via NAND gate 156, disabling IC 120, which disables the system. IC 166is also an oscillator-divider, which is used as a time delay for up toseveral minutes, during which time the system is disabled. This delayrepresents a nuisance factor for would-be car thieves and can beadjusted for any reasonable length of time or for no delay.

Referring now also to FIG. 9, there is shown analog circuitry comprisinga pulser circuit, shown generally at reference numeral 210, andreceiver/amplifier circuitry, shown generally at reference numeral 212.The pulser circuit 210 provides excitation for the SAW device 34 (FIG.4). The excitation is in the form of a single cycle, relatively shortpulse of approximately 10 volts in the preferred embodiment.

The Q5 signal generated by the digital circuitry shown in FIG. 8 aboveis applied to the pulser circuit 210, as shown. In particular, the Q5 isapplied to a 100 pf capacitor 214, which is connected to a PNPtransistor 216. Also applied to the transistor 216 is a 10 volt powersupply.

A coupling coil 42 is connected to the transistor 216 and to ground. Thecoupling coil 42 of the receiver/amplifier circuit 212 is shown in themechanical drawing of FIG. 4. This coupling coil 42 is adapted both totransmit a 10 volt pulse and to receive a much weaker response signalthereto from the SAW device shortly thereafter. That is, although thecoupling coil 42 is driven with a 10 volt pulse, the same coupling coilthen functions as an antenna to receive a signal that is only on theorder of a few millivolts, which response signal occurs on the order ofa few hundred nanoseconds after the excitation pulse. This millivoltresponse signal must be amplified by the amplifier circuit 212.

A clamping and resistor isolation mechanism is provided in the amplifier212 to eliminate or screen the 10 volt pulse and to amplify the smallerresponse signal. A 100 ohm resistor R1 is connected to the coupling coil42. Connected to the other terminal of resistor R1 is a capacitor C1.And connected to the other terminal of capacitor C1 is an emitterfollower transistor Q1 coupled to a common emitter amplifier transistorQ2 through a diode D1.

Transistors Q4 and Q5 are standard common emitter amplifier stagesconnected to one another in a suitable manner to amplify the signal to alevel sufficiently high to drive the digital logic circuitry shown inFIG. 8.

In operation, when signal Q5 goes low, it is differentiated by capacitor214 to drive PNP transistor 216. Transistor 216 drives the coupling coil42 with a single 10 volt pulse at the beginning of each read cycle.

As mentioned hereinabove, resistor R1 provides isolation for the 10 voltpulse. Capacitor C1 provides AC coupling and DC blocking. Emitterfollower transistor Q1 drives common emitter amplifier transistor Q2through diode D1. The voltage drop in diode D4 allows the emittervoltage of transistor Q3 to be the same level as that of the collectorof transistor Q2. With decoupled DC feedback through resistors R2 andR3, the voltage at the base of transistor Q1, collector of transistor Q2and emitter of transistor Q3 is the same. This allows the use offeedback diodes D2 and D3 for clamping. Transistor Q2 provides "pulldown" drive and transistor Q3 provides "pull up" drive for sufficientclamping.

Referring now also to FIG. 10, there is shown a flow chart of systemoperation. It will also be helpful to refer to FIGS. 11 and 12, whichdepict timing diagrams of signals generated by components depicted inFIG. 8 and whose reference numerals are cited adjacent the timing linesin the FIGURES. The Q5 and Q9 signals refer to those generated by IC120.

Initially, the system is energized, step 300, by the motor vehiclebattery, not shown. The ignition key, including the SAW device imbeddedtherein, is excited, step 310.

The SAW device (FIG. 6) receives an electromagnetic energy pulse via itscoil or antenna 36. The entire array is energized along the bus bars 62and 64. The launch transducer 50 generates surface electroacoustic wavesalong the piezoelectric substrate in the direction of the transmissionline 66. After a time equal to the propagation time for such waves alongthe blank portion of the transmission line, the electroacoustic acousticwaves are reconverted to electromagnetic energy and reradiateelectromagnetic waves via the coupling coil 36. Thus, the code containedin the SAW device is captured, step 320.

Once the code is captured, it is compared with a code stored in thecomputer processor 16 (FIG. 1) of the motor vehicle, not shown, step330. In another part of the processor 16, the code is tested, step 340.If the code captured from the SAW device key 26 compares favorably withthe code stored in the processor 16, the motor vehicle can be startedand operated, step 350. If, however, the captured code and the storedcode are unsuccessfully compared, the motor vehicle cannot be started,step 360.

In the preferred embodiment, a predetermined time, such as threeminutes, must follow the attempted use of a key 26 having encodedtherein an incorrect code. In alternate embodiments, however, the timeperiod can be lengthened, shortened or even eliminated.

Since other modifications and changes varied to fit particular operatingrequirements and environments will be apparent to those skilled in theart, the invention is not considered limited to the example chosen forpurposes of disclosure, and covers all changes and modifications whichdo not constitute departures from the true spirit and scope of thisinvention.

What is claimed is:
 1. A motor vehicle access system comprising:(a)signal generating means for generating an uncoded signal; (b) couplingmeans operatively connected to said signal generating means forconverting said uncoded signal to an uncoded electromagnetic signal; (c)a surface acoustical wave (SAW) device operatively connected to saidcoupling means for receiving said uncoded electromagnetic signaltherefrom, converting said uncoded electromagnetic signal to a codedsurface acoustic wave and transferring said coded surface acoustic waveto said coupling means for generating a coded electromagnetic replysignal; (d) amplifying means operatively connected to said couplingmeans for amplifying said coded electromagnetic reply signal; (e)comparing means operatively connected to said amplifying means forcomparing said coded reply signal to a previously stored code; and (f)enabling means operatively connected to said comparing means forenabling operation of a motor vehicle when said code and said codedreply signal are successfully compared.
 2. The motor vehicle accesssystem in accordance with claim 1 wherein said uncoded signal generatedby said signal generating means has substantially greater voltage thansaid coded reply signal.
 3. The motor vehicle access system inaccordance with claim 2 wherein said amplifying means comprisesisolating means for screening said uncoded signal generated by saidsignal generating means so that said coded reply can be suitablyamplified.
 4. The motor vehicle access system in accordance with claim 2wherein said signal generating means generates a single cycle pulse. 5.The motor vehicle access system in accordance with claim 1 wherein saidcoded reply signal comprises a binary code.
 6. The motor vehicle accesssystem in accordance with claim 5 wherein said binary code is a 6-bitcode.
 7. The motor vehicle access system in accordance with claim 1wherein said enabling means generates a VEHICLE START ENABLE signal. 8.The motor vehicle access system in accordance with claim 1 wherein saidcomparing means comprises means to decode said coded reply signal apredetermined number of times.
 9. The motor vehicle access system inaccordance with claim 8 wherein said decoding means comprises anoscillator.
 10. A circuit for coded access to a motor vehiclecomprising:(a) signal generating means for generating an uncoded signal;(b) a pair of coupling coils for transferring uncoded and coded signal,respectively, to and from a SAW device; (c) a surface acoustical wave(SAW) device operatively connected to said signal generating means viasaid coupling coils for receiving an uncoded signal therefrom,converting said uncoded signal to a coded surface acoustical wave andreconverting said coded surface acoustical wave to a reply signal; (d)decoding means operatively connected to said SAW device for decodingsaid reply signal to provide an access code; (e) comparing meansoperatively connected to said decoding means for comparing said accesscode to a prior code; and (f) enabling means operatively connected tosaid comparing means for enabling operation of a motor vehicle when saidaccess code and said prior code are successfully compared.
 11. Thecircuit in accordance with claim 10 wherein said signal generated bysaid signal generating means has substantially greater voltage than saidreply signal.
 12. The circuit in accordance with claim 11 wherein saidsignal generating means generates a single cycle pulse.
 13. The circuitin accordance with claim 10 wherein said reply signal comprises a binarycode.
 14. The circuit in accordance with claim 13 wherein said binarycode is a 6-bit code.
 15. The circuit in accordance with claim 10wherein said enabling means generates a VEHICLE START ENABLE signal. 16.The circuit in accordance with claim 10 wherein said decoding meanscomprises means to decode said reply signal a predetermined number oftimes.
 17. The circuit in accordance with claim 10 wherein said decodingmeans comprises an oscillator.
 18. A circuit for identifying an operatorof a motor vehicle to provide authorized operation thereof,comprising:(a) an uncoded signal generating means connected to a firstcoil for transferring said uncoded signal; (b) a second coil connectedto a surface acoustical wave (SAW) device for receiving said uncodedsignal when said first and second coils are brought into proximity witheach other, said second coil actuating said SAW device to provide acoded surface acoustic signal which is reconverted to a coded replysignal that is transferred back to said first coil; (c) amplifying meansoperatively connected to said first coil for amplifying said coded replysignal; (d) decoding means operatively connected to said amplifyingmeans for decoding said reply signal to provide an access code; and (e)enabling means operatively connected to said decoding means for enablingoperation of a motor vehicle when said access code matches a storedcode.
 19. The circuit in accordance with claim 18 wherein said signalgenerated by said signal generating means has substantially greatervoltage than said reply signal.
 20. The circuit in accordance with claim19 wherein said amplifying means comprises isolating means for screeningsaid signal generated by said signal generating means so that said replysignal can be suitably amplified.
 21. The circuit in accordance withclaim 19 wherein said signal generating means generates a single cyclepulse.
 22. The circuit in accordance with claim 18 wherein said replysignal comprises a binary code.
 23. The circuit in accordance with claim22 wherein said binary code is a 6-bit code.
 24. The circuit inaccordance with claim 18 wherein said enabling means generates a VEHICLESTART ENABLE signal.
 25. The circuit in accordance with claim 18 whereinsaid decoding means comprises means to decode said reply signal apredetermined number of times.
 26. The circuit in accordance with claim18 wherein said decoding means comprises an oscillator.
 27. A circuitfor accessing a motor vehicle comprising:(a) a first coil and a secondcoil proximately disposed thereto, said first coil supplying said secondcoil with an electromagnetic signal when said second coil is movedrelative thereto, said second coil being connected to a surfaceacoustical wave (SAW) device for receiving said electromagnetic signalfrom said first coil propagating a surface acoustic wave in said SAWdevice for generating a coded reply signal that is transferred back tosaid second coil via said first coil; (b) amplifying means operativelyconnected to said first coil for amplifying said coded reply signal; (c)decoding means operatively connected to said amplifying means fordecoding said coded reply signal to provide an access code; (d)comparing means operatively connected to said decoding means forcomparing said access code to a stored code; and (e) enabling meansoperatively connected to said comparing means for enabling operation ofa motor vehicle when said access code and said stored code aresuccessfully compared.
 28. The circuit in accordance with claim 27wherein said signal received by said SAW has substantially greatervoltage than said reply signal.
 29. The circuit in accordance with claim28 wherein said amplifying means comprises isolating means for screeningsaid signal received by said SAW device so that said reply signal can besuitably amplified.
 30. The circuit in accordance with claim 27 whereinsaid reply signal comprises a binary code.
 31. The circuit in accordancewith claim 30 wherein said binary code is a 6-bit code.
 32. The circuitin accordance with claim 27 wherein said enabling means generates aVEHICLE START ENABLE signal.
 33. The circuit in accordance with claim 27wherein said decoding means comprises means to decode said reply signala predetermined number of times.
 34. The circuit in accordance withclaim 27 wherein said decoding means comprises an oscillator.
 35. Acoded access ignition system for an automobile, comprising:(a) areceptacle for receiving in proximity thereto a surface acoustical wavedevice; (b) a self-propagating surface acoustical wave (SAW) device forgenerating an access code for said automobile, said access code beinggenerated and self-propagated by relative movement of said SAW devicewith respect to said receptacle; and (c) validation means operativelyconnected to said receptacle for determining said SAW device access codeand generating a signal indicative of a validation of said access codein comparison with a stored code of matching value.